And I'm Robert Siegel. In Arizona, shock is giving way to sadness and deep appreciation for the 19 firefighters killed battling the Yarnell Hill wildfire on Sunday. A candlelight vigil is being held this evening in the city of Prescott, home of the Granite Mountain Hotshots. All of the firefighters killed were part of that unit. Karen Takai is with the Southwest Incident Management team, the federal unit now in charge.

KAREN TAKAI: Every day is a very difficult day for us as we transitioned into this fire. We start the mornings with just recognizing the fact that it's an incredible tragedy that's happened out here and yet, we need to get focused back on the task at hand.

SIEGEL: The task at hand is getting a handle on the Yarnell Hill fire, which rages on completely uncontained. It has burned more than 8,000 acres. The formal inquiry into Sunday's deaths is beginning in earnest, as well. A federal investigative team is on its way to the area. In a moment, we'll hear from a former Hotshot firefighter about the kind of work these crews do.

But first, we'll get the latest from NPR's Kirk Siegler, who joins us from near the town of Yarnell. Kirk, what are the investigators coming into and what do we know about the circumstances that led to this tragedy?

KIRK SIEGLER, BYLINE: Robert, really a lot more questions than answers still, I'm afraid. We do know is that this interagency federal fire investigative team is going to be combing through literally everything, including whether the Hotshot crew had ample warning and whether they were in a position where there was an escape route if and when things got bad, and for how long contact was lost between these firefighters and whomever was coordinating their attack, which we can presume was focused on keeping the flames away from homes and buildings in and around the town.

I've been told that there was a fire behavior analyst on duty up there on Sunday. Now, that person would have been able to predict, to the best of their abilities anyway, where the fire was headed. But, Robert, as we know, things apparently just became very, very chaotic up there.

SIEGEL: Well, is there a timeline for the investigation? And how long do these things typically take?

SIEGLER: Well, these types of investigations do take a lot of time. We were told today to not expect even a preliminary report for at least a week or more. You know, this is the worst incident involving wildland firefighter fatalities since 1933 in the U.S. There's going to be a lot of attention paid to this investigation, a lot of scrutiny. And you can bet that investigators will be taking a lot of time.

The other thing, Robert, that fire managers are telling me more generally about the circumstances of this fire, you know, like so many others we've been reporting on recently in the Southwest where natural fires haven't been allowed to burn and there's prolonged drought and rising temperatures.

You know, these types of wildfires at any moment can burn so hot, so intense and things can change so quickly and become so dangerous at any moment that, you know, in the end, we can't always predict everything, fire managers are reminding us. And we certainly can't control Mother Nature, either.

SIEGEL: And the fire continues to burn. It's not at all contained. What's the latest on the effort to control it?

SIEGLER: Right. There are two big stories to report here. This fire, as you say, is still burning out of control. I've spent the day, today, much of the day at a roadblock here. I've been watching helicopters over on the horizon carrying water over to the fire. There's a lot of smoke and haze here. And there's even a chance, a chance that the winds may gust up to 80 miles an hour over the next few hours.

Crews are mobilizing to this fire by the minute, many coming from other large fires in Colorado, so there's not far to go. You know, aside from the tragic deaths of the firefighters we've been talking about, we still don't yet even know the extent of the damage the fire has done itself in and around the town of Yarnell. And, Robert, there's no estimate of when this fire will even be contained, let alone controlled.